It is estimated that over 170 million people worldwide are infected with the Hepatitis C virus (HCV). With an estimated human sero-prevalence of 3% globally, HCV is the major cause for most cases of non-A, non-B hepatitis, (Alberti, A. et al., J. Hepatology 31, (Suppl. 1): 17-24, 1999). While the symptoms of acute hepatitis subside in some patients, at least 85% of HCV infections become chronic, and 20% of those infected develop liver cirrhosis. There is less than a 50% survival rate at four years post cirrhosis diagnosis. Chronic HCV infection is also associated with increased incidence of hepatocellular carcinoma.
HCV is a positive-stranded RNA virus whose genome encodes a polyprotein of approximately 3000 amino acids. This precursor protein is processed into at least 10 viral structural and nonstructural proteins: C, E1, E2, p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B (Blight, K. J., et al., Antiviral Ther. 3, Suppl. 3: 71-81, 1998). HCV nonstructural (NS) proteins are derived by proteolytic cleavage of the polyprotein and are presumed to provide the essential catalytic machinery for viral replication.
NS3 is an approximately 68 Kda protein, and has both an N-terminal serine protease domain and an RNA-dependent ATPase domain at its C-terminus. It has been shown that the NS4A protein serves as a co-factor for the serine protease activity of NS3. NS3 functions as a proteolytic enzyme that cleaves sites liberating other nonstructural proteins necessary for HCV replication and is a viable therapeutic target for antiviral chemotherapy.
No vaccines are available for HCV, and the established therapy of interferon treatment is effective in only 15-20% of patients (Weiland, O., FEMS Microbiol. Rev. 14: 279-88, 1994), and has significant side effects (Walker, M. A., et al., DDT 4: 518-29, 1999; Moradpour, D., et al., Eur. J. Gastroenterol. Hepatol. 11: 1199-1202, 1999). While the current standard of care, pegylated interferon α in combination with ribavirin, is more efficacious and appears to decrease hepatocellular carcinoma in patients with HCV-related cirrhosis (Hung, C. H., et al., J Viral Hepatitis 13(6): 409-414, 2006), this treatment has also been shown to produce side effects such as thyroid dysfunction (Huang, J. F., et al., J Viral Hepatitis 13(6): 396-401, 2006).
The poor prognosis for patients suffering from HCV infection and the current lack of effective, approved treatments, highlights the overwhelming need for new inhibitors of HCV NS3 protease.